The goal of this UH2 and UH3 is to study how exosomes can deliver siRNAs across the blood brain barrier to enter neurons and other brain cells. The immediate target is the mutant huntingtin mRNA. Huntington's disease (HD) is caused by an increase in the CAG trinucleotide repeats to 36 in series; it necessitates years in a high level nursing facility because of neurodegeneration first in striatum and cortex and then to other brain structures. HD patients have cognitive impairment, depression and aberrant movements. Most HD patient present by 30 to 40 years of age; a few have a juvenile onset. A rational treatment is to decrease expression of mutant huntingtin mRNA; this therapeutic can be accomplished in HD mouse models by siRNA, antisense oligonucleotides (ASO) and adeno-associated virus (AAV) with shRNAmir directed against huntingtin mRNA. However, delivery remains a pitfall to practical implementation of the therapeutics. siRNA and ASO require long-term infusion. In non-human primates, ASO administered to spinal fluid does not reach the striatum and spread of siRNA is limited in brain. Although promising, AAV-shRNA requires several injections into brain areas and the shRNAmir is unregulated. A gap in HD therapeutics can be filled by microvesicles normally extruded by cells, exosomes. Exosomes with rabies virus glycoprotein (RVG) on their surface can be injected into the blood, cross the blood brain barrier, and enter neurons and glia. RVG-exosomes can carry siRNA cargo. Delivered into the blood circulation, the exosomes deposit siRNA in neurons to engage in RNA interference. Our purpose is to develop exosomes as a therapeutic in HD. The UH2 examines the ability of RVG-exosomes carrying siRNA against huntingtin mRNA to cross the blood brain barrier to enter neurons. Localization in brain and RNAi dependent knock down will be studied. Hyper-functional siRNAs will be sought. Because exosomes are made from cytoplasm of cells, exosome mRNA, miRNA, and implaced siRNA will be identified by deep sequencing. Immune reactivity and immune-neutralization will be studied, since exosomes have potential antigens, like RVG, and will need to be administrated often. The UH3 further establishes exosome-based therapeutics, by study of reversal or prevention of neuropathology and aberrant movement in HD mouse models. Dosing of exosomes will be secured. A team of experts in HD pathogenesis, siRNA development, RNA identification and measurement, RNAi mechanisms and exosome production and brain delivery will carry out the studies. Harnessing exosomes for brain delivery is expected to form a viable therapeutic to reduce expression of mutant huntingtin in patients with HD. Patients with other genetically- based neurodegeneration will benefit.